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Title:Proton binding and aluminum complexation by soil humic and fulvic acids
Author(s):Vance, George Floyd
Doctoral Committee Chair(s):Stevenson, Frank J.
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Agriculture, Agronomy
Abstract:An investigation was conducted on proton binding and aluminum complexation using six humic and fulvic acids. Potentiometry was used in the proton binding study to characterize acidic functional groups and configurational properties. Separation of weak and strong acidic functional groups by different computational methods was inconclusive, pointing out the difficulties associated with characterizing these weak acid polyelectrolytes by potentiometric titration. Configurational changes, influenced by intramolecular H-bonding, were more prominent with the high-molecular-weight humic acids than the low-molecular-weight fulvic acids. The assumption of a normal distribution of acidic functional groups was found to be valid but only at high ionic strength (e.g., I = 0.1) and was attributed to an equalizing effect caused by the addition of neutral salt. Factors of pH and ionic strength, rather than humic concentration, were of significance in modeling proton dissociation constants for the humic and fulvic acids.
Complexation of aluminum by humic and fulvic acids was examined by use of three titration methods: (1) standard base titration, (2) pH stat in which base consumed per aluminum addition was measured, and (3) sequential aluminum addition in which pH was monitored after aluminum additions. The latter two methods were found useful for determining stability constants for aluminum-humate complexes. Results using the base titration method were inconclusive. Overall stability constants for 1:2 and 1:3 complexes of aluminum with humic and fulvic acids, respectively, ranged from 0.98-1.43 and 0.25-0.62 for pB$\sb2\sp\star$ and 1.88-2.77 and 0.77-1.07 for pB$\sb3\sp\star$. A chemical equilibrium model was derived for predicting organic bound forms of aluminum. At natural levels of aluminum (0.01-1 ppm), and dissolved organic carbon (2-50 ppm DOC), an increasing proportion of the aluminum existed in organic bound forms with increases in pH (between 3-7) and dissolved organic carbon.
Issue Date:1990
Rights Information:Copyright 1990 Vance, George Floyd
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9021771
OCLC Identifier:(UMI)AAI9021771

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